The invention relates to a seal for the clearance between an opening and a shaft passing therethrough.
A known seal has an outer ring made of a rigid material for mounting liquid-tight in an opening in a structure. The inside of the outer ring has an inwardly-open groove having two axial boundary surfaces. An inner ring is made of an elastic material and supported at the groove on a shaft passing through the opening for rotation with the shaft. The inner ring has two, radially outwardly projecting flanges which flank a cylindrical midsection for each flange to be associated with one of the boundary surfaces.
A seal of this type is described in German patent publication No. DOS 26 14 888. It is not intended for continuous operation but merely for a safety measure in a normally-unsealed clearance between the propeller shaft and a bulkhead of a ship. In the rare, for example sinking, cases when it is exposed to water on one side, the water flows into the interior of the seal, between the flanges, and there produces sufficient pressure to force the flange on the low-pressure side sealingly against the boundary surface with which it is associated. The deformation of the flange for sealing is, therefore, a direct function of the pressure differential between the high- and low-pressure sides of the seal. As a result, low or no pressure differential renders the use of such a seal difficult or impossible.
Moreover, the extent of flange deformation necessary to force it sealingly against the boundary surface of the outer ring is dependent on the spacing therebetween. If the spacing is variable or imprecisely set, the seal may respond unreliably. It is, therefore, necessary to set the spacing very precisely and to prevent variation of the spacing during operation from, for example, axial shaft excursions. This gives rise to further difficulties in connection with the practical use of such a seal.